MXPA00010296A

MXPA00010296A - Membrane which comprises a blend of a polysulphone or a polyether sulphone and polyethylene oxide/polypropylene oxide substituted ethylene diamine

Info

Publication number: MXPA00010296A
Application number: MXPA/A/2000/010296A
Authority: MX
Inventors: Martin Heijnen
Original assignee: Kalsep Limited
Priority date: 1998-04-23
Filing date: 2000-10-20
Publication date: 2002-06-05

Abstract

A membrane which can be used in membrane filtration processes and which has a reduced tendency to fouling is a polysulphone or a plyether sulphone and a polyethylene oxide/polypropylene oxide substituted diamine and can be made by a phase inversion process in the presence of pore modifying agents such as an alcohol, glycerol or glycol to give a membrane which has a pore size of 0.1&mgr;to 1 micron and is hydrophilic.

Description

MEMBRANE THAT COMPRISES A MIXTURE OF A POLYSULPHONE OR A POLYETERSULPHONE AND ETHYLENDIAMINE REPLACED WITH OXIDE POLYETHYLENE / POLYPROPYLENE OXIDE DESCRIPTION OF THE INVENTION The present invention relates to a membrane that can be used in membrane filtration processes that include microfiltration, ultrafiltration and reverse osmosis and that has a reduced tendency to become soiled. Membranes are used in separation techniques such as filtration, microfiltration, reverse osmosis, etc. and for the recovery of solids. The membranes can be made of polymeric material and a particular class of polymers are the polysulfones, including the polyethersulfones. Polysulfones have been widely used because of their chemical resistance and good physical properties. "Polysulfone" is used as a generic name for a type of high molecular weight polymer that contains an aromatic nucleus and sulfone groups in the main chain. A normal sulfone is formed as the condensation product of bisphenol A 'and dichloro-diphenyl sulfone. Polyethersulfones are also widely used, Ref: 124210 polyphenylsulphones and polyarylethersulfones. However, the polysulfones have a surface that is hydrophobic and, in use, polysulfone membranes are prone to fouling, particularly when used to filter liquids containing organic components as a proteinaceous material. This fouling results in the formation of a layer on the surface of the membrane that blocks the pores of the membrane and causes deterioration in its execution. It is known to treat the surface of hydrophobic membranes to form a more hydrophilic surface and a method is described in US Patent No. 4,618,553. Another method of treating a membrane to make it more hydrophilic is described in the PCT International Application WO 90/14149. However, the methods described above of modifying the hydrophobic membranes to produce a more hydrophilic surface can be relatively complex and expensive and be limited in their effectiveness. Patent EP 0407665A1 discloses a polyethersulfone membrane made of polyethersulfone and other polymeric components and a method of making the mixtures by dissolving the polymeric components in n-methylpyrrolidone (NMP), dimethylformamide (DMF) or dimethylacetamide and co-precipitating the polymer mixture by means of of a phase inversion process using water. Patent application WO 96/27429 describes a membrane comprising a mixture of a polysulfone or polyethersulfone and a copolymer of ethylene oxide / propylene oxide. We have now divided mixed polysulfone / polyethersulfone membranes with improved properties and a method of making the membranes. According to the invention there is provided a membrane comprising a mixture of a polysulfone or a polyethersulfone and a diamine substituted with polyethylene oxide / polypropylene oxide of the formula (I) where Ri, R2, R3 and R are the same or different polyoxyethylene and / or polyoxypropylene radicals of the formula (II) ? - (III) where X, XI, Y and Yl can be the same or different from each of Ri, 2 R3 and R4. Preferably the compound (1) has an average molecular weight weight of from 400 to 100,000 and more preferably from 1,650 to 50,000 and X, Y, XI, Yl are therefore selected. The compounds of formula (I) can be made by the sequential addition of propylene oxide and ethylene oxide to ethylenediamine. The compounds (I) are sold under the Registered Trade Mark "Tetronics" by BASF or as "Poloxamers" or "Superonics" by ICI and are commercially available. The preferred compounds (I) are those in which Ri, R2, R3 and R4 are of the formula (II) ie the end groups are polyoxyethylene. The polysulfone can be any polysulfone that can be produced in the form of a film, membrane, hollow fiber or other configuration that is conventionally used and the preferred polysulfones are standard polysulfones and polyethersulfones. Polysulfones are described in U.S. Patent No. 4230,463. Polysulfones have aromatic hydrocarbyls that generally contain radicals that have good thermal stability. The polysulfones and polyethersulfones suitable for making the membranes have molecular weights in the range of 20,000 to 80,000 and are sold under the trade names UDEL, P-1700 and P-3500 by Amoco, ASTREL 360 Plastic by the 3M Company and as Polysulfone Ultrasons S and Polysulfone Ultrason E, by BASF. The molar ratio of polysulfone to the diamine substituted with polyethylene oxide / polypropylene oxide in the compound is preferably from 25: 1 to 1:40 and more preferably from 8: 1 to 1:30. The membranes of the present invention preferably have a structure such that the diamine molecules substituted with ethylene oxide / propylene oxide copolymer are concentrated towards the surface of the membrane, so that the more hydrophilic copolymer molecules cause the surface of the material is present more hydrophilic with little or no loss in membrane performance. A part of the ethylene oxide / propylene oxide copolymer molecule may have a higher affinity with the dissolved polysulfone polymer and a part (the more hydrophilic part) may have a higher affinity in the non-solvent phase. By a variation of the substituted diamine of copolymer with ethylene oxide / propylene oxide the properties of the final composition can be varied. The ethylene oxide / propylene oxide copolymer chains preferably have a proportion of the ethylene oxide to propylene oxide groups such that the copolymer is substantially water soluble although it is compatible with the polysulfone in the solvent solution.

The molar ratio of the ethylene oxide to propylene oxide groups in the side chains of ethylene oxide / propylene oxide copolymer is preferably from 1:10 to 10: 1. The mixtures can be prepared by dissolving both polymer components in a solvent and co-precipitating the mixture by a phase inversion process. The solvent for the polymers should be one which is inert to the polymers and dissolves both polymers for example n-methylpyrrolidone, dimethylformamide, dimethylacetamide and the like. The membranes of the present invention have a pore size preferably with a cutoff of molecular weight greater than 500 and preferably the membranes of the present invention have a pore size with a cutoff of molecular weight greater than 1,000 and with a pore size above of 1 miera (lμ). We have surprisingly found that the addition of pore modifying agents to the solution of the polymers can produce membranes with an increased pore size. The pore modifying agents that can be used are non-solvents such as water, alcohols such as n-butanol, polyethylene glycols (PEG), glycerols, and polyvinylpyrrolidones (PVP).

The polyethylene glycol is preferably present in an amount above 80% polymer solution, the PVP above 50%, the butanol above the %, glycerols above 20% and water above 15%. It is very surprising that the addition of these compounds to the solution of the polymers does not make the solution unstable and causes an increase in the pore size. This is particularly true in the case of polymers such as PVP and PEG. It has also been found that the use of the additives can result in a membrane with a more open pore structure which is referred to as a tortuous pore structure. The process that is used to precipitate the polymer mixture of the solution is the precipitation by the process of phase inversion of the solution of the components (solution of polymeric mixture) using a precipitation liquid. Preferably the ethylene oxide / propylene oxide copolymer is enriched on the surface of the membrane bound in the phase inversion process, due to migration of the water soluble component of the colloidal interface. It is thought that the copolymer and ethylene oxide / propylene oxide polysulfone are coprecipitated from the solvent and, due to the more hydrophilic nature of the ethylene oxide chain of the migra copolymer to the liquid solvent / precipitation interface that enriches the surface of the formed membrane. It is thought that the ethylene oxide / propylene oxide copolymer molecules are aligned with their hydrophilic component aligned to liquid precipitation and the non-hydrophilic part aligned to the hydrophilic polysulfone polymer matrix that enriches the surface of the membrane to make it more hydrophilic . The incorporation of the substituted diamine of copolymer with ethylene oxide / propylene oxide within the polysulfone polymer matrix is indicated by the fact that the diamine substituted with ethylene oxide / propylene oxide copolymer can not be removed by repeated washing . EP 0407665A discloses water as the precipitation liquid, but it was surprisingly found that, if certain agents are added to the precipitation liquid membranes, they are produced with a larger pore size. The pore-enlarging agents that can be used are the low molecular weight alcohols such as methanol, ethanol, polyethylene glycols, glycerols, solvents such as NMP, DMF, dimethylacetamide and the like.

The amount of these pore enlargement agents present in the precipitation liquid can be greater than 100% (ie, above the precipitation liquid) in the case of alcohols and glycerols and above 90% in the case of polyethylene glycols and up to 80% in the case of solvents. Optionally, after the formation of the composition comprising the polysulfone and the ethylene oxide / propylene oxide copolymer, the copolymer, or other polymeric additive can be crosslinked. The crosslinking can be carried out using an appropriate crosslinking agent. The crosslinking agents which can be used are sodium hypochlorite, isocyanates, dicarboxylic acid halides, chlorine-treated epoxides such as epichlorohydrin, the crosslinking can also be obtained by UV radiation, for example by the use of iso-buironitrile and subsequent reaction with some species appropriate divalents. The degree of crosslinking can be controlled by the type and concentration of the crosslinking agent, the duration of the treatment and the temperature. The most severe crosslinking treatment, the highest molecular weight of the final crosslinked product. After crosslinking, the membrane is preferably washed to remove excess unreacted ethylene / propylene oxide copolymer.

The crosslink virtually eliminates any possibility of leaching the copolymer. The membranes of the invention may be of the conventional type for example in the form of sheets, tubes, hollow fibers, etc. It is a feature of the membranes of the invention that the hydrophilicity of a polysulfone membrane can be permanently increased with little or no deleterious effect on its filtration function. This increased hydrophilicity will reduce the tendency of the membrane to get dirty. An additional feature of the membranes of the invention is that they have advantages when used in microfiltration or ultrafiltration. In microfiltration and ultrafiltration it is important that the membranes are moistened before being used, that is to say, the pores are filled with air filling up with liquid. With polysulfones this is difficult when they have a low hydrophilicity and in use they can involve difficulty for pre-wetting the polysulfone membrane with a liquid with a low surface tension, for example alcohol and testing to ensure that the membrane is completely pre-moistened before it can be used in aqueous filtration. The membranes of the present invention, due to the more hydrophilic nature of the membranes, can be moistened with water so that they can be used in ultrafiltration and microfiltration and, in particular, the microfiltration membranes are instantly moistened by contacting with water, and after the repeated drying. Typically the microfiltration membranes are provided dried and moistened for use, and it is a feature of the invention that micro-filtration membranes can be produced which can be dried and subjected to repeated drying without ruining the structure. The micro-filtration membranes of the present invention generally have a pore size of 0.1 μm to 1 μm and are hydrophilic. The process of the present invention can also produce membranes with a "tortuous" structure, this means that the membranes have a structure similar to a sponge, preferably a macrovoidal structure and that can allow filtration capacity greater than that obtained. In a tortuous structure there is an interconnection of polymeric branches that form a reticulated open cellular matrix and so that the membranes have a greater null space.

The invention will now be described with reference to the following examples wherein Example 1 is of a membrane prepared by the process of EP 0407 665A1.

Example 1 A polyethersulfone sold under the tradename of Ultrason E and a copolymer of ethylene oxide / propylene oxide of molecular weight of 18,000 (Tetronic 1307) are dissolved in n-methylpyrrolidone (NMP) and stirred until a clear solution. The solution was formed in a hollow fiber membrane by a spinning process. The weight of the composition of the solution was 25% polyethersulfone (PES), 20% ethylene oxide / propylene oxide copolymer and 55% n-methylpyrrolidone. The membranes formed in water were washed for two days after the formation. The membrane made according to the Example had a molecular weight cutoff of about 50,000. It was tested for antifouling properties in a milky filtration test where the milk was filtered through the membrane and the flow of clean water was measured. The membrane was cleaned by washing it with clean water at the end of each day and the flow of clean water was measured.

The results are shown in Figure 1. The initial clean water flow was 230 lm-2 hr "/ bar". After each wash, the flow of clean water was restored close to its original value. At the end of the fourth day a low level concentration was used to prevent the milk from leaving during the weekend and this almost completely restored the flow to its original value at 220 lm "2 hr'Vbar" 1. The process flow of 80 lm "2hr" 1 / bar "1 was maintained at a constant level through the test, indicating that virtually no fouling of the membrane had occurred. The results of Figure 1 can be compared with the results of a commercially available polyethersulfone membrane of good quality, also with a cut-off of about 50,000 shown in Figure 2. The commercially available membrane had an initial water flow greater than 500 lm ~ 2hr "1 / bar" 1 compared to 230 lm "2hr'1 / bar" 1 for the membrane of the Example. However, the initial process flow was much lower at 40 lm "2hr" 1 / bar "1 compared to 80 lm" 2hr "1 / bar" 1 for the membrane of the Example. For the commercially available membrane that is cleaned with water, it did not restore the flow of water to a satisfactory level and, on the following day, the flow of the process was also declined. Due to the fouling that occurred, this membrane was left in a diluted sodium hypochlorite solution during the weekend after day two. Although this slightly improved the flow of clean water, it did not restore the flow close to its original value and the flow of the subsequent process was also rejected at 22 lm "2hr" 1 / bar "1. At the end of day three it was ineffective to wash with water to improve the flow of clean water, showing that the membrane had become seriously dirty.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims

CLAIMS Having described the invention as above, the contents of the following claims are claimed as properties: 1. A membrane characterized in that it comprises a mixture of a polysulfone or a polyethersulphone and a diamine substituted with polyethylene oxide / polypropylene oxide of the formula (I) Where Ri, R2, R3, and R4 are the same or different polyoxyethylene and / or polyoxypropylene radicals of the formula H- (OCH 2CH2) "Yl- (II) (III) where X, XI, Y and Yl can be the same or different in each of Ri, R2, R3 and R4.
2. A membrane according to claim 1, characterized in that the compound (I) has an average molecular weight of 400 to 100,000 and therefore X, Y, XI, Yl are chosen.
3. A membrane according to claim 1, characterized in that the compound (i) has an average molecular weight of 1,650 to 50,000 and therefore X, Y, XI, Yl are chosen.
4. A membrane according to any of claims 1 to 3, characterized in that the compounds of the formula (I) are prepared by the sequential addition of propylene oxide and ethylene oxide to ethylenediamine.
5. A membrane according to any of claims 1 to 4, characterized in that the compounds (?) Are those in which Ri, R2, R3 and R4 are of the formula (II).
6. A membrane according to any of claims 1 to 5, characterized in that the polysulfone has a molecular weight in the range of 20,000 to 80,000. A membrane according to any of claims 1 to 6, characterized in that the molar ratio of polysulfone in the diamine substituted with polyethylene oxide / polypropylene oxide is from 25: 1 to 1:40. 8. A membrane according to any of claims 1 to 6, characterized in that the molar ratio of polysulfone in the diamine substituted with polyethylene oxide / polypropylene oxide is from 8: 1 to 1:30. according to any one of claims 1 to 8, characterized in that it has a structure such that the diamine molecules substituted with ethylene oxide / propylene oxide copolymer are concentrated towards the surface of the membrane 10. A membrane according to any of Claims 1 to 9, characterized in that the ethylene oxide / propylene oxide copolymer chains have a proportion of ethylene oxide for the propylene oxide groups such that the copolymer is substantially soluble in water while still being compatible with the polysulfone in the solvent solution 11. A membrane according to claim 10, characterized in that the molar ratio of the ethylene to the propylene oxide groups in the ethylene oxide / propylene oxide copolymer side chains is from 1:10 to 10: 1. 12. A membrane according to any of claims 1 to 11, characterized in that it has a pore size with a molecular weight cutoff of greater than 500. 13. A membrane according to any of claims 1 to 12, characterized in that it has a pore size with a molecular weight cut-off greater than 1000. 14. A membrane according to any of claims 1 to 13, characterized in that it has a pore size of 0.1 μ to 1 miera and that it is hydrophilic. 15. A method of making a membrane according to any of the preceding claims, characterized in that it comprises dissolving both polymeric components in a solvent and coprecipitating the mixture. 16. A method according to claim 15, characterized in that the solvent for the polymers is n-methylpyrrolidone, dimethylformamide, dimethylacetamide and similar compounds. 17. A method according to claim 15 or 16, characterized in that the pore modifying agents are added to the solution of the polymers. 18. A method according to claim 17, characterized in that the pore modifying agent is water, alcohol, methanol, ethanol, n-butanol, polyethylene glycol (PEG), glycerol, polyvinylpyrrolidones (PVP) or a solvent such as NMP, DMF or dimethylacetamide. 19. A method according to claim 16 or 17, characterized in that the pore modifying agent is present in an amount of up to 100% of the solvent. 20. A method according to claim 17, characterized in that the pore modifying agent is polyethylene glycol which is present in an amount of up to 80% of the polymer solution. 21. A method according to claim 17, characterized in that the pore modifying agent is PVP which is present in an amount of up to 50% of the polymer solution. 22. A method according to claim 17, characterized in that the pore modifying agent is butanol which is present in an amount of up to 20% of the polymer solution. 23. A method according to claim 17, characterized in that the pore modifying agent is glycerol which is present in an amount of up to 20% of the polymer solution. 24. A method according to claim 17, characterized in that the pore modifying agent is water that is present in an amount of up to 15% of the polymer solution. 25. A method according to any of claims 15 to 24, characterized in that the process that is used to precipitate the polymer mixture from the solution is the precipitation by the phase inversion process of the solution of the components (solution of polymer mixture) using a precipitation liquid. 26. A method according to any of claims 15 to 25, characterized in that after the formation of the composition comprising the polysulfone and the ethylene oxide / propylene oxide copolymer, the copolymer or other polymeric additive is crosslinked. 27. A method according to claim 26, characterized in that the membrane is washed after crosslinking, to remove excess unreacted ethylene oxide / propylene oxide copolymer.